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I   I

The most effective test is obtained by machine, of which
Professor Thurston's (Fig. 578) is probably the best. A is a
pendulum hanging on the test journal B, whose brasses can be
adjusted for any pressure by turning the screw D E against the
spring c, while P shews the value, both totally and per square
inch. The thermometer G indicates the temperature. The
journal being rotated towards the right, the pendulum moves to
the left, together with pointer F, and the scale K at once indicates
the friction per sq. in. of journal, so that

__ P's graduation.

^ ~~ P's graduation.

Every five minutes during a test the revolutions, temperature, and
graduations are noted, values of p, afterwards found, and the results
plotted as curves wherever possible. In his ' railroad' machine,
Prof. Thurston used a full-sized locomotive journal.

Lubrication.—The oil-bath gives the best result, but is
rarely found in practice. The self-lubricating bearing, Fig. 5 79, is
perhaps the next best, where the oil is lifted by the shaft collar
and distributed by a wiper. The next in order is the oil pad, as
contained in the locomotive axle-box, Fig. 580, the bush merely
embracing the top half of the journal. Usually lubricators have
to be fitted, and are then designed for the conditions. B, Fig. 270,
p. 266, is a common syphon lubricator. The oil level being below
the syphon-pipe, a piece of cotton wick is placed in the latter and
hangs over in the oil. The fluid then rises by capillarity; and the
wick is to be removed when the machinery is stopped, otherwise
there is unnecessary loss of oil. Leuvain's needle lubricator, A,
Fig. 581, is a glass vessel, filled with oil, closed by a wooden plug
and inverted. Within the stopper a 'needle' fits freely, and the
oil trickles down the latter only when vibrated by the shaft. If
the dropping of the oil is to be observed and its regulation
obtained, such a lubricator as the Crosby sight-feed at B, Fig. 581,
may be adopted. When handle a is vertical, the valve <£ is
raised, and adjustment given by the nut d; but when a is horizontal,
b is closed, and the supply stopped

A loose pulley may be fed with tallow by means of Stauffer's
screw-down lubricator c. Oil would only fly away by centrifugal